This invention relates in general to prosthetic devices, and in particular to prosthetic ankles.
As shown in FIG. 1, leg amputees often regain significant walking capability by using a walking system A including a pylon B rigidly connected to a prosthetic foot C. Unfortunately, many of these amputees experience instability while walking. One reason for this is that the prosthetic foot C is not flat on the ground at heel strike, and does not fall flat until just prior to lift off when the amputee""s weight W is coming off the prosthetic foot C. Prior to that time, the amputee""s weight W is largely supported by the heel D of the prosthetic foot C. Many amputees also find these rigid walking systems uncomfortable because of a lack of cushioning at heel strike.
As shown in FIG. 2, prosthetists have attempted to alleviate the uncomfortable nature of rigid walking systems by inserting a resilient ankle E between the pylon B and the prosthetic foot C. Unfortunately, this has exacerbated the instability problem. The inventors have determined that the amputee""s weight W at heel strike causes the toe T of the prosthetic foot C to pivot upward toward the pylon B rather than downward to the ground. As a result, the prosthetic foot C fails to fall flat for an even longer portion of the amputee""s gait than with rigid walking systems.
Therefore, there is a need in the art for a walking system that places prosthetic feet flat on the ground at an earlier time during a step to provide amputees with improved stability.
An inventive walking system includes a prosthetic ankle comprising an upper leg connected to a lower end of a pylon and a lower leg connected to an upper surface of a prosthetic foot. An interconnecting member interconnects the upper and lower legs so the legs rotate about a medial/lateral axis positioned forward of the pylon. The interconnecting member resiliently biases the legs apart from one another so the legs are positioned in a spaced-apart relationship with respect to one another when the person""s weight is off the prosthetic ankle. Also, the legs rotate toward one another about the medial/lateral axis when the person""s weight is placed on the prosthetic ankle at heel strike, thereby allowing a toe of the prosthetic foot to rotate toward the ground at heel strike. As a result, the prosthetic foot falls flat on the ground soon after its heel strikes the ground. The inventive walking system thus provides improved stability.